refactor: a better way to have maybe-importable third-party modules

2 files changed, 8 insertions, 6 deletions

diff --git a/coverage/misc.py b/coverage/misc.py
index 1e4b4e74..bd1767ca 100644
--- a/coverage/misc.py
+++ b/coverage/misc.py
@@ -83,14 +83,16 @@ def import_third_party(modname):
         modname (str): the name of the module to import.
 
     Returns:
-        The imported module, or None if the module couldn't be imported.
+        The imported module, and a boolean indicating if the module could be imported.
+
+    If the boolean is False, the module returned is not the one you want: don't use it.
 
     """
     with sys_modules_saved():
         try:
-            return importlib.import_module(modname)
+            return importlib.import_module(modname), True
         except ImportError:
-            return None
+            return sys, False
 
 
 def nice_pair(pair):
diff --git a/coverage/tomlconfig.py b/coverage/tomlconfig.py
index 31cd0bb0..737c728c 100644
--- a/coverage/tomlconfig.py
+++ b/coverage/tomlconfig.py
@@ -5,7 +5,6 @@
 
 import os
 import re
-import sys
 
 from typing import Any, Callable, Dict, Iterable, List, Optional, Tuple, Type, TypeVar
 
@@ -17,9 +16,10 @@ from coverage.types import TConfigSection, TConfigValue
 
 if env.PYVERSION >= (3, 11, 0, "alpha", 7):
     import tomllib      # pylint: disable=import-error
+    has_tomllib = True
 else:
     # TOML support on Python 3.10 and below is an install-time extra option.
-    tomllib = import_third_party("tomli")
+    tomllib, has_tomllib = import_third_party("tomli")
 
 
 class TomlDecodeError(Exception):
@@ -51,7 +51,7 @@ class TomlConfigParser:
                 toml_text = fp.read()
         except OSError:
             return []
-        if sys.version_info >= (3, 11) or tomllib is not None:
+        if has_tomllib:
             try:
                 self.data = tomllib.loads(toml_text)
             except tomllib.TOMLDecodeError as err: